I have two of these case saddles. I have seen a couple of these for sale online, but I do not believe they are made anymore.

With this piece you can insert an instrument case - ukulele size to dreadnought size guitar. It then makes it possible to carry it as a backpack. There is a padded back piece and shoulder straps. Please research these on line as Crossrock CRCS1

These came to me as a part of a deal and I will never use them - so they are not unpacked.

I have two of these and would like to sell each of them for $30 - plus shipping.